JP7406302B2 - Method of dispensing material onto a substrate using a solenoid valve of a pneumatically driven dispensing unit - Google Patents

Description

TECHNICAL FIELD This disclosure relates generally to apparatus and methods for dispensing viscous materials onto substrates, such as printed circuit boards.

Viscous material dispensers with dispensing pumps that dispense electronic materials operate in a variety of ways. Some well-known dispensing pumps use a servo motor to drive a rotary auger, while some dispense pumps use a linear servo motor to drive a piston. . Other dispensing pumps do not use electric servo motors, but instead rely on other actuation means. One such dispensing pump disclosed in U.S. Pat. It works by compressing a spring and then releasing air pressure, allowing the spring to accelerate the piston and push it back until it abuts the valve seat. With this dispensing unit, a droplet of material is forced out of an orifice in the valve seat when the piston contacts the valve seat. Such dispensing units typically use solenoid valves to control the flow of air (or other gas) into and out of the piston chamber.

It is well known in the dispensing industry that dispensers respond differently when repeatedly operated drop by drop than when they are repeatedly operated to produce a periodic series of droplets in rapid succession. ing. In particular, the first droplet, or even the first few drops, within a periodic series of droplets may differ from the balance of droplets within the periodic series of droplets. , is well known, although not fully understood. For example, the first few drops may contain less mass of material than the later deposited drops.

Figures 1 and 2 show two known solenoid drive circuits used to apply voltage to the coil. Prior art solenoid drive circuits typically use an on/off drive circuit to apply voltage to the coil. Some prior art circuits (see U.S. Pat. No. 5,300,302 to Gieffers) improve upon the simple on-state or off-state by adding another discrete level of drive voltage (or current). This supplemental drive level provides the current required to hold the coil in the energized position at a level lower than that used to quickly transition the solenoid from the unenergized position to the activated position. (i.e., the holding current is lower than the pull-in current). This lower drive level saves energy and serves to suppress coil heating compared to simpler on/off drive circuits, and the time required for the solenoid field to dissipate when the solenoid is switched off. The operating speed can be improved by minimizing the time.

U.S. Patent No. 5,747,102 U.S. Patent No. 3,116,441

One aspect of the present disclosure relates to a method of controlling a dispensing unit used to dispense material onto a substrate. In one embodiment, the method includes connecting a solenoid coil of a pneumatically driven pump to an amplifier output of a dispensing system, and driving the solenoid coil with the amplifier to cause the pneumatically driven pump to dispense material onto the substrate. including causing.

Embodiments of the method may further include directing an idle current to flow in the solenoid coil during periods of inactivity. The idle current may be sufficient to cause warming of the solenoid coil, but still insufficient to drive the solenoid to the actuated position. The method includes directing a first current level to flow in the solenoid coil to quickly actuate the solenoid and directing a second current level to flow in the solenoid coil after the solenoid is actuated. It can further include. The second current level may be sufficient to maintain the solenoid in an activated state. The second current level may be lower than the first current level. The method may further include directing a third current level flowing within the solenoid coil. The third current level is of opposite polarity to the second current level and may be of a sufficiently small magnitude that it does not actuate the solenoid. The method may further include directing an idle current to flow in the solenoid coil during periods of inactivity. The idle current may be sufficient to cause warming of the solenoid coil, but still insufficient to drive the solenoid to the actuated position. The dispensing unit may be configured to dispense the viscous material onto the electronic substrate.

The accompanying drawings are not intended to be drawn to scale. In the drawings, each identical or nearly identical component that is illustrated in various figures is represented by a like numeral. For clarity, not all components may be labeled in all drawings.

1 is a circuit diagram of a prior art bipolar junction transistor (BJT) that switches current in a solenoid coil; FIG. FIG. 2 is a circuit diagram of a field effect transistor (FET) that switches the current in a solenoid coil. 1 is a schematic diagram of a dispenser of one embodiment of the present disclosure; FIG. FIG. 2 is a circuit diagram of an actuator drive circuit having an amplifier that drives current in a solenoid coil. FIG. 7 is a graph showing the position of the dispensing unit versus time when no idle current is used. FIG. 2 is a graph showing the position of the dispensing unit versus time when using an idle current of 0.1 ampere (A).

BRIEF DESCRIPTION OF THE DRAWINGS The present disclosure will now be described in detail, by way of example only and without limitation in generality, with reference to the accompanying drawings, in which: FIG. This disclosure, with respect to its applications, is not limited to the details of construction or the arrangement of components shown in the following description or the drawings. The principles described in this disclosure are capable of other embodiments and of being practiced or carried out in various ways. Additionally, the language and terminology used herein is for purposes of explanation and should not be considered limiting. The use of the terms "comprises," "comprising," "having," "containing," "accompaniing" and variations thereof herein refers to the preceding description. It is meant to include the items listed above, as well as their equivalents and additional items.

Various embodiments of the present disclosure relate to viscous material dispensing systems and apparatus including dispensing systems. Embodiments disclosed herein relate to techniques for dispensing materials onto electronic substrates by a dispensing pump configured to control the electrical current flowing in the coil of an air solenoid valve to a desired level.

FIG. 3 schematically depicts a dispenser, indicated generally at 10, according to one embodiment of the present disclosure. The dispenser 10 is configured to apply a viscous material (e.g., adhesive, encapsulant, epoxy, solder paste, underfill material, etc.) or semi-viscous material (e.g., solder flux, etc.) onto an electronic substrate 12, such as a printed circuit board or a semiconductor wafer. used for dispensing. Dispenser 10 may alternatively be used in other applications, such as for dispensing automotive gasket materials, or for certain medical applications, or for dispensing conductive inks. I can do it. It is to be understood that, as used herein, reference to viscous or semi-viscous materials is exemplary and not intended to be limiting. Dispenser 10 includes first and second dispensing units, indicated generally at 14 and 16, respectively, and a controller 18 that controls operation of the dispenser. It should also be understood that a dispensing unit may also be referred to herein as a dispensing pump and/or a dispensing head. Although two dispensing units are shown, it should be understood that more than one dispensing unit may be provided.

The dispenser 10 also includes a frame 20 having a base or support 22 that supports the substrate 12, and a dispensing unit gantry 24 movably coupled to the frame 20 to support and move the dispensing units 14, 16. For example, as part of the calibration procedure, a weighing device or scale 26 may be included to weigh the dispensed amount of viscous material and provide weight data to the controller 18. Other transfer mechanisms, such as a conveyor system (not shown) or a moving beam, may be used in the dispenser 10 to control loading and unloading of substrates from the dispenser. The gantry 24 can be moved using a motor under the control of the controller 18 to position the dispensing units 14, 16 at predetermined locations above the substrate. Dispenser 10 may include a display unit 28 connected to controller 18 and providing various information to the operator. An optional second controller may be provided to control the dispensing unit. Each of the dispensing units 14 and 16 is also configured to use a z-axis sensor to detect the height at which the dispensing unit is placed above the electronic board 12 or above the mechanism mounted on the electronic board. can do. The z-axis sensor is coupled to controller 18 and relays information acquired by the sensor to the controller.

Before performing a dispensing operation as described above, a board, e.g. a printed circuit board, must be positioned or aligned with the dispenser of the dispensing system. The dispenser further includes a vision system 30. In one embodiment, the vision system is coupled to a vision system gantry 32 that supports and moves the vision system. A vision system gantry is movably coupled to frame 20. This embodiment is also shown in FIG. In another embodiment, vision system 30 may be provided on dispensing unit gantry 24. As mentioned above, vision system 30 is utilized to locate landmarks or components, known as fiducials, on the substrate. Once the location is determined, the controller can be programmed to manipulate the movement of one or more of the dispensing units 14, 16 to dispense material onto the electronic board.

The systems and methods of the present disclosure relate to dispensing materials onto a substrate, such as a circuit board. The description of the systems and methods provided herein refers to an exemplary electronic board 12 (eg, a printed circuit board) supported on support 22 of dispenser 10. In one embodiment, the dispensing operation is controlled by controller 18, which may include a computer system configured to control the material dispenser. In another embodiment, controller 18 may be operated by an operator. To obtain one or more images of electronic board 12, controller 18 is configured to manipulate movement of vision system gantry 32 and move the vision system. To perform a dispensing operation, the controller 18 is further configured to manipulate the movement of the dispensing unit gantry 24 and move the dispensing units 14, 16.

Embodiments of the present disclosure provide for dispensing units 14, 16, etc. having an actuator control circuit configured to control the current flowing in the coil of the air solenoid valve to (substantially) any desired level. Note Regarding units. Specifically, referring to FIG. 4, an actuator drive circuit, indicated generally at 40, is configured to drive current into a solenoid coil 42 of a solenoid valve, indicated generally at 44, using a PWM transconductance amplifier 46. The PWM transconductance amplifier uses the input voltage to direct and control the current in the load. Although a transconductance amplifier 46 is shown and described herein, other types of amplifiers may be used to achieve the results achieved with transconductance amplifiers. In one embodiment, the solenoid coil 42 of the solenoid valve 44 is connected as a load for an amplifier 46, either directly to the amplifier or through an intervening filter component 48, such as a high frequency choke inductor. . In other words, the current control is part of an analog control system rather than a digital (on/off) control system typically found in other coil drive systems, and this additional control is utilized to Better achieve system goals. For example, the advantage of lower holding voltage can also be realized with analog amplifier control without the need for any special or additional circuitry.

As shown, the amplifier 46 is coupled to the controller 18 to control the operation of an actuator control circuit 40, and more particularly a solenoid valve 44, which is comprised of a solenoid coil 42 and an air valve 50. is configured to drive the operation of the dispensing units 14, 16. Solenoid valve 44 is configured to control the flow of air to an air cylinder 52 that is coupled to a piston 54 that is pneumatically driven from a lower (first) position to an upper (second) position. . Piston 54 engages valve seat 56 and dispenses material onto substrate 12. Specifically, solenoid valve 44 is configured to control air flow to air cylinder 52 and piston 54. Controller 18 is coupled to amplifier 46 and configured to generate an instruction signal to the amplifier to control the current in solenoid coil 42 .

By providing complete analog control over the current waveform of solenoid coil 42, numerous features of solenoid valve 44 can be modified or adjusted to better meet the particular requirements of the dispensing system. For example, holding the solenoid coil 42 in an on state with a low holding current may minimize the time required for the solenoid field to dissipate when the solenoid valve 44 is switched off. Regarding the actuator control circuit 40 of embodiments of the present disclosure, in order to more quickly and actively drive the field strength to a near zero state (off state), By directing a slightly negative current, the time required for the magnetic field of solenoid coil 42 to dissipate (ie, switch the solenoid off) can be further reduced.

Another advantage of actuator drive circuit 40 relates to the fact that the time required for current to build up in a coil or other inductor is inversely proportional to the available supply voltage (di/dt=V/L). In prior art on/off systems, the resistance of the coil windings and the rated supply voltage are selected such that the power dissipated in the solenoid coil 42 is within the coil's rating. The use of current control amplifier 46 allows the use of a supply voltage higher than the rated voltage of solenoid coil 42. For example, by driving a 24V coil from a 48V power supply (rather than from a 24V power supply), the current in the solenoid coil 42 may be increased twice as fast, but only until the current is twice the rated current. The power loss will be four times the nominal value. By using the current control amplifier 46, the desired current can be directed at its maximum rated value, and the amplifier can rapidly increase the current in the solenoid coil 42 using the maximum available supply voltage. But it still limits the current when it reaches the commanded value.

In this context, "analog control system" refers to a digital-to-analog converter (DAC) that provides pseudo-analog control through digital circuitry and is capable of producing hundreds or thousands of small discrete levels within a given range. ) and digitally controlled amplifiers, such as amplifiers using analog-to-digital converters (ADCs). For example, a 12-bit DAC can provide 4096 discrete levels and is sometimes referred to as "analog control" to distinguish it from two-level or three-level on/off control systems. Furthermore, the known systems referenced above use bipolar junction transistors (BJTs) or field effect transistors (FETs) to control the current in the solenoid coil 42, and such transistors can also be used in amplifiers. Alternatively, the use of transistors in on/off circuits, such as transistors in known systems, although they may themselves be considered amplifiers, in either saturation (on) or cutoff (off) conditions Characterized by operating transistors. This mode of operation is significantly different from the function of amplifier 46, and its flexibility and advantages are discussed herein. In amplifiers, such as PWM transconductance amplifier 46, used in embodiments of the present disclosure, the transistors are rapidly alternated between saturation and cutoff states to minimize the power dissipated in the transistors. However, this switching occurs at a frequency high enough that substantially all of the energy at the switching frequency and its harmonics can be filtered out before reaching the load. The remaining direct current (DC) and low frequency energy passes through the filter and reaches the load. In this configuration, even if the transistor is utilized only in its on or off state, the functionality of the amplifier subsystem provides the functionality and advantages of an analog amplifier but without the drawbacks, especially the known on/off state. There are no system restrictions.

Significant commercial benefits of using amplifier 46 to drive solenoid coil 42 are realized when it is recognized that many existing dispensers drive the dispense unit as a servomotor mechanism. Utilizing this existing infrastructure greatly facilitates field deployment of solenoid-controlled pneumatically driven pumps. Solenoid valve 44 can typically be connected to the same connector that supports servo-driven pumps, minimizing system changes to accommodate different pump types. To use known solenoid control systems in systems that are also designed to support servo motor controlled dispensing pumps, there is both an amplifier for the servo motor control and also a separate solenoid coil drive system. A combination would be required to support the drive of both pump types.

A further embodiment of the present disclosure provides a droplet between the dispensing of the first droplet or first few drops within a series of droplets and the dispensing of subsequent drops within the series of droplets. Concerning methods for minimizing differences in dispensing behavior. The power dissipated in the coil varies with cycle frequency, the temperature of the coil varies with the power dissipated in the coil, and the winding resistance of the coil varies with coil temperature, so that the response of the coil is It is observed that it may vary with the winding resistance of the coil. You can refer to the following:
Cycle frequency → dissipated power → coil temperature → winding resistance → solenoid response

When the coil is activated for a first period of time after an extended period of disuse, the coil is at a different temperature than when periodically subsequent drops are dispensed. Therefore, if the coil temperature can be more tightly controlled, the response of the coil can be made more consistent. Embodiments of the method further include driving the solenoid coil with an amplifier such that the on and off switching times are faster than those achieved with prior art driving methods.

In one embodiment, the disclosed method can control the current flowing in the coil of an air solenoid valve to (substantially) any desired level. Specifically, the method includes driving current into a coil with a PWM transconductance amplifier of a dispensing unit, the dispensing unit using the input voltage to direct and control the current in the load. . As mentioned above, other types of amplifiers can be used to achieve the same benefits. In one embodiment, the solenoid valve coil is connected as a load for the amplifier, either directly to the amplifier or through an intervening filter component such as a high frequency choke inductor. The amplifier configuration allows current to be controlled to flow at a low steady state level when the valve is not actively operating. This level can be selected to be low enough not to activate the valve, but still sufficient to keep the coil warm. In other words, the current control is part of an analog control system, rather than the digital (on/off) control system typically found in known coil drive systems, and this additional control is utilized to Better achieve system goals. The advantage of lower holding voltage can also be realized with analog amplifier control.

Some known systems recognize the advantage of maintaining the temperature of solenoid coils (see US Pat. No. 8,339,762 to North). However, such known systems use short pulses to dissipate a certain amount of energy in the coil without applying voltage to the solenoid in the on position.

In one method, the coil is designed for 24V and has a resistance of about 15 ohms at 25°C, resulting in a current of 1.6 amps. As the coil warms up, the resistance will increase and the current will decrease. A controlled actuation current of 1.4A causes the valve to operate substantially as fast as with higher currents, thus minimizing unnecessary winding heating. Once activated, the coil remains in its activated position until the current drops below about 300 mA. Below this level, this particular coil will return to a no-voltage state. Furthermore, by holding the current at a level well below this holding current threshold, the valve will not return to its energized state.

An idle current of approximately 0.1 A has the advantageous effect of increasing the idle temperature of the coil. This low "background" current generates enough heat to warm the coil to a temperature higher than its surroundings, yet does not interfere with normal operation of the coil. In practice, the level of idle current required to produce the same steady-state temperature in the coil depends on ambient conditions, the coil's thermal time constant, the coil's normal cyclic operating speed, as well as other similar factors. It will depend on factors and variables.

When comparing the position versus time response of the poppet in the air valve, the presence of a low level "idle current" in the coil can substantially reduce or even eliminate the difference in the first actuation response. . Referring to Figures 5 and 6, the third trace represents the movement of the solenoid poppet. It can be seen that the response of the valve in FIG. 6 is much more consistent, correcting the disorganized trace seen in FIG. 5 due to the first pulse response.

As shown in Figures 5 and 6, the first trace represents the current indication, the second trace represents the trigger, the third trace represents the poppet position, and the fourth trace represents the piston position. These traces were captured in continuous mode using a digital oscilloscope and traces from 10 events were superimposed. As seen in the third set of traces in Figure 5, one event response is different from the other responses in the set of sweeps, and this is the first event after a period of inactivity (i.e., the first drop). ). It can also be seen in the fourth trace that the piston responds differently to this change in poppet response. In FIG. 6, where an idle current in the coil is introduced and in the third set of traces representing the poppet response, it is clear that all the poppet response curves are substantially the same. The small amount of variation that remains in piston response is due to other causes.

Having thus described certain aspects of at least one embodiment of the present disclosure, it is to be understood that various modifications, changes, and improvements will readily occur to those skilled in the art. Such alterations, modifications, and improvements are intended to be part of this disclosure, and are intended to be within the spirit and scope of the invention. Accordingly, the foregoing description and drawings are only examples.
[Configuration 1]
In a method of controlling a dispensing unit used to dispense material onto a substrate,
Connect the solenoid coil of the pneumatically driven pump to the output of the dispensing system amplifier;
The solenoid coil is driven by the amplifier to dispense material onto the substrate by the pneumatically driven pump.
[Configuration 2]
2. The method of claim 1, further comprising passing an idle current through the solenoid coil during periods of inactivity.
[Configuration 3]
3. The method of configuration 2, wherein the idle current is sufficient to cause warming of the solenoid coil, but still insufficient to drive the solenoid to the actuated position.
[Configuration 4]
directing a first current level through the solenoid coil to rapidly actuate the solenoid;
and directing a second current level through the solenoid coil after the solenoid is actuated.
[Configuration 5]
5. The method of configuration 4, wherein the second current level is sufficient to maintain the solenoid in an activated state.
[Configuration 6]
6. The method of configuration 5, wherein the second current level is lower than the first current level.
[Configuration 7]
7. The method of claim 6, further comprising directing a third current level flowing within the solenoid coil.
[Configuration 8]
8. The method of claim 7, wherein the third current level is of opposite polarity to the second current level and of a magnitude sufficiently small to not actuate the solenoid.
[Configuration 9]
9. The method of claim 8, further comprising directing an idle current to flow in the solenoid coil during periods of inactivity.
[Configuration 10]
10. The method of configuration 9, wherein the idle current is sufficient to cause warming of the solenoid coil, but still insufficient to drive the solenoid to the actuated position.
[Configuration 11]
2. The method of configuration 1, wherein the dispensing unit is configured to dispense a viscous material onto an electronic substrate.

10 Dispenser 12 Electronic board 14 Dispensing unit 16 Dispensing unit 18 Controller 20 Frame 22 Support 24 Dispensing unit gantry 26 Measuring instrument 28 Display unit 30 Vision system 32 Vision system gantry 40 Actuator control circuit 42 Solenoid coil 44 Solenoid valve 46 Current Control amplifier 48 Filter component 50 Air valve 52 Air cylinder 54 Piston 56 Valve seat

Claims (4)

In a method of controlling a dispensing unit used to dispense material onto a substrate,
Connect the solenoid coil of the pneumatically driven pump to the output of the dispensing system amplifier;
driving the solenoid coil with the amplifier to cause the pneumatically driven pump to dispense material onto the substrate;
passing an idle current through the solenoid coil during periods of inactivity;
A method,
the idle current warms the solenoid coil to a temperature higher than ambient but still does not drive the solenoid to an actuated position;
Furthermore,
directing a first current level through the solenoid coil to rapidly actuate the solenoid;
directing a second current level flowing within the solenoid coil after the solenoid is activated;
including;
the second current level is sufficient to maintain the solenoid in an activated state;
the second current level is lower than the first current level;
Method. The method of claim 1 , further comprising directing a third current level flowing within the solenoid coil. 3. The method of claim 2 , wherein the third current level is of opposite polarity to the second current level and of a magnitude sufficiently small to not actuate the solenoid. 2. The method of claim 1, wherein the dispensing unit is configured to dispense viscous material onto an electronic substrate.

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